Re: Concorde's Engines

Date:         18 Jun 99 01:39:26 
From:         w_keller@gmx.de (Wolfgang Keller)
Organization: Customer of UUNET Deutschland GmbH, Dortmund, Germany
References:   1 2 3 4
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Gregory Travis <greg@sherrill.kiva.net> wrote:

> How does the >INLET< produce thrust?

My fluid dynamics classes were quite some time ago, but something I
still remember is:

F = m_dot * (v_2 - v_1)

Where F is the thrust generated by some kind of air-breathing engine
(positiv in the direction opposite to v_1 and v_2), m_dot is the air
flow through the engine (approximation: fuel mass set to 0), v_2 is the
exhaust speed and v_1 the speed at the inlet.

Now, if we only take the inlet itself, v_2 is smaller than v_1, because
the air is slowed down. Thus, the inlet can not produce thrust, it
always generates drag. To generate thrust, you need to accelerate air,
not slow it down.

Regards,

--
Wolfgang Keller

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